Analyses for lead

Everson J, Patterson CC. 1980. "Ultra-clean" isotope dilution/mass spectrometric analyses for lead in human blood plasma indicate that most reported values are artificially high. Clin Chem 26 1603-1607. 

In the UK the Joint Food Science and Safety Group of the Department of Health and the Ministry of Agriculture, Fisheries and Food have published the results of many analyses for chemical contaminants in food carried out under their Food Surveillance Programme. In many cases the raw data from these surveys are available for analysis. Table 2.1 lists the results of analyses for lead in some samples of cow, sheep and pig kidney obtained in Scotland and England.5 There are clear differences between species and some evidence of differences between sampling locations. What is not clear is the extent to which the variability observed is due to real and consistent differences between species and location or to normal biological variation. 

The main radiation source for AAS is the hollow-cathode lamp (HCL). The HCL (Fig. 27.3) emits radiation characteristic of a particular element. The choice of HCL for AAS is simple. For example, if you are analysing for lead, you will need a lead-coated HCL. It is normal to pre-warm the HCL for about 10 min prior to use. This can be done either by using a separate pre-... 

If you were analysing for lead in a sample, which hollow-cathode lamp... 

Chemically synthesized Cu(II)-containing PMT is used as the working electrode of a 3-electrode system in a thin layer amperometric cell unit to detect ionic analytes in an aqueous stream by flow injection analyses. The electrode response is linearly dependent on the applied voltage. The electrode possesses favorable sensitivity and stability in comparison to other metallic electrodes such as steel and platinum [794]. The incorporation of mercury into PMT results in an effective electrode for the analyses for lead(II) ions in aqueous media (detection limit 0.05 ppm). The mercury films are deposited electro-chemically after the electropolymerization step [795]. 

Duggan, M.J., Williams, S., 1977. Lead in dust in city streets. Sci. Total Environ. 7, 91—97. Everson, J., Patterson, C.C., 1980. Ultra-clean isotope dilution/mass spectrometric analyses for lead in human blood plasma indicate that most reported values are artificially high. Clin. Chem. 26, 1603-1607. 

As evident in the preceding formula, lead concentration measurements by IDMS must also consider the isotopic compositions of lead in the unspiked sample (Huemann 1988). These include natural isotopic variations among samples and isotopic fractionation during the analysis. The latter correction, which is common to all elemental analyses by IDMS, is addressed with standard techniques using certified standard reference materials (e.g., NIST SRM 981). The former correction, which is necessary for few heavy elements besides lead, requries separate isotopic analyses of unspiked samples. This in turn necessitates additional analyses for lead concentration measurements. 

The analytical research and development (R D) unit is often responsible for the preparation and vahdation of test methods. The R D lab is not faced with the same pressures for rapid analysis as the QC unit, where pending results often hold up production. In addition, R D often assigns personnel to specific instmments or techniques, whereas QC generally requires technicians to perform varied analyses. This leads to an expertise on the part of analytical chemists and technicians which is difficult to duphcate in QC. Therefore the R D test method should be mgged enough to withstand the different environment of the QC lab and stiU provide vahd results. 

The effect of accumulation in various systems depends greatly on the quantity of pollutants involved. Many pollutants can be detected at concentrations lower than those necessary to affect human health. For pollutants which are eliminated slowly, individuals can be monitored over long periods of time to detect trends in body burden the results of these analyses can then be related to total pollutant exposure. Following are two examples of air pollutants that contribute to the total body burden for lead and carbon monoxide. 

D. Task-specific hazard analyses must lead to the development of written standard operating procedures (SOPs) that specify the controls necessary to safely perform each task. Detailed hazard analyses conducted for each site task and operation provide the basis for developing SOPs to protect employees from safety and health hazards. Written SOPs provide a mechanism for informing employees of procedures that ensure their safety and for enabling management to enforce hazard control procedures. 

Electrolytic Mg is less pure than Mg obtained by thermal reduction methods and is purified commercially by sublimation under vacuum, a process inherent in thermal reduction. Typical analyses for crude electrolytic Mg (assay 99.8%), for sublimed material (assay 99.95%) and for twice sublimed material (assay 99.99%) are collected in Table l. Sublimation reduces most impurity levels (by 10 ) but leads to increased Zn content. 

Tin(IV) antimonate is an inorganic cation exchanger with high selectivity for lead ions20. This may be useful for trace analyses that are sensitive to lead interference. 

LLE has been used in the past for the extraction of pesticides from environmental water samples [17]. However, its application in the extraction of waste-water samples is scarce due to the low efficiency of extraction, especially for polar analytes. Because of the vast amount of surfactants and natural products present in wastewater samples, emulsions are formed which complicate the process of extraction and lead to low extraction recoveries. However, there have been some useful applications of LLE to wastewater analyses. For example, LLE was found to be effective for the isolation of herbicide and pesticide organic compounds from industrial wastewater samples and also from complex matrices [18]. 

Wiedmeyer (1998). One method of testing for interference is to examine the survey data. In this type of analysis a large number of points are recorded across the mass range, rather than a single measurement taken at a particular mass number for each element. Figure 9.5 shows survey data (dashed line) for masses 203 to 210 on a sample believed to contain lead. The natural lead isotopic abundance is superimposed, shown by filled columns. The proximity of the survey data to the actual abundance of lead indicates that lead is present, and that no interfering elements are present. In this case, a single measurement at mass 208 (which is used for most analyses of lead) is sufficient to quantify lead in the sample. 

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